Typically, glass fibers are formed by drawing molten glass into filaments through a bushing or orifice plate and applying an aqueous sizing composition containing lubricants, coupling agents, and film-forming binder resins to the filaments. The sizing composition provides protection to the fibers from interfilament abrasion and promotes compatibility between the glass fibers and the matrix in which the glass fibers are to be used. After the sizing composition is applied, the fibers may be gathered into one or more strands and wound into a package or chopped while wet and collected. The collected continuous strands or chopped strands can then be dried or the chopped strands may be packaged in their wet condition as wet chopped fiber strands (WUCS). The chopped strands may contain hundreds or thousands of individual glass fibers. The steps taken in conjunction with the fibers depend upon the ultimate use of the glass fibers.
Wet chopped fibers are conventionally used in wet-laid processes in which the wet chopped fibers are dispersed in a water slurry that contains surfactants, viscosity modifiers, defoaming agents, and/or other chemical agents. The slurry containing the chopped fibers is then agitated so that the fibers become dispersed throughout the slurry. The slurry containing the fibers is deposited onto a moving screen where a substantial portion of the water is removed to form a web. A binder is then applied, and the resulting mat is dried to remove any remaining water and cure the binder. The formed non-woven mat is an assembly of dispersed, individual glass filaments.
The sizing composition applied to wet chopped fibers used in wet-laid processes to form non-woven mats generally contains polyvinyl alcohol as the film forming agent. The polyvinyl alcohol functions as a processing aid and protects the glass fibers from breaking during the formation of the fibers. However, once the fibers are chopped and placed into the white water, the polyvinyl alcohol tends to wash off the fibers into the white water. In the white water, the polyvinyl alcohol precipitates out of solution. This precipitate can be detrimental to the manufacturing line in that the precipitate can clog the tanks. In such a situation, the manufacturing line must be stopped to clean the tanks and remove the precipitate. Additionally, the polyvinyl alcohol can cause storage problems, particularly in warm environments. As water evaporates from the sizing composition, the polyvinyl alcohol tends to form a film covering the surface of the aqueous composition within the storage container. Further, the large number of hydroxyl groups present in the polyvinyl alcohol encourages undesirable microbe activity in the storage containers.
Sizing compositions that do not contain polyvinyl alcohol for fibers used in a wet-laid process currently exist in the art. Non-limiting examples of such polyvinyl alcohol-free sizing compositions are set forth below.
U.S. Pat. No. 4,461,804 to Motsinger, et al. discloses an aqueous sizing composition that includes a cationic lubricant, an amide compound, and a water soluble or dispersible polyol. The sizing composition is used to produce wet chopped size glass fiber strands that are subsequently used to form non-woven glass fiber mats by a wet-laid process. The water dispersible or water soluble polyols comprise a major amount of the solids of the sizing composition. The cationic lubricant forms a minor amount of the solids. Optionally, one or more silane coupling agents may be included in the size composition.
U.S. Pat. Nos. 4,592,956 and 4,681,802 to Gaa, et al. teach a treating composition that includes (1) one or more soluble, dispersible, and/or emulsifiable cationic lubricants having one or more primary, secondary, and/or tertiary amines, (2) one or more water soluble poly(oxyethylene-oxyalkylene) copolymers having a molecular weight of at least 15,000 and a weight ratio of ethylene oxide to hydrophobic alkylene oxide in the range from about 99 to 1, (3) one or more coupling agents having an organic and an inorganic polar functional moiety, and (4) water. The treating composition also preferably includes one or more starches that are less than completely soluble in cold water. The treating composition can be applied to any type of glass fiber and used in a wet-laid process.
U.S. Pat. No. 4,681,658 to Hsu, et al. discloses glass fibers treated with a composition that includes a nonionic surfactant and a cationic quaternary ammonium salt surfactant. The composition may be added simultaneously or sequentially with chopped fibers to an aqueous media (white water). Alternatively, the treating composition may be applied to glass fibers, which may then be formed into wet or dry chopped glass fibers. When the composition is used to treat glass fibers, a carrier such as water is added to the composition. One or more moderately water soluble, water dispersible, or water emulsifiable polyols such a polyvinyl alcohol may optionally be included in the composition. The treated glass fibers are used to form non-woven, sheet-like mats by any known method, including a wet-laid process. The glass fiber mats may be used as a replacement for felt in shingles or for use in built-up roofing systems.
U.S. Pat. No. 4,810,576 to Gaa, et al. teaches an aqueous chemical treatment for glass fibers that contains (1) an ungelled polymer that is capable of forming a film at a temperature below ambient temperature and has a molecular weight of at least 100,000 and up to 6,000,000, (2) one or more aldehyde-condensate reactable polymeric agents, (3) an aldehyde-condensate reactable organosilane coupling agent, (4) one or more water soluble, dispersible or emulsifiable cationic lubricant surfactants having one or more primary, secondary, and/or tertiary amine moieties, and (5) a carrier. The treating composition can be prepared by any method known in the art and applied to glass fibers by conventional methods. The treated glass fibers may be used to form a non-woven, sheet-like mat of treated chopped glass fibers by a wet-laid process.
U.S. Patent Publication 2007/0059506 to Hager, et al. discloses a sizing composition that includes one or more film forming agents (such as a polyurethane film former, a polyester film former, and/or an epoxy resin film former), at least one lubricant, and at least one silane coupling agent (such as an aminosilane or methacryloxy silane coupling agent). When needed, a weak acid such as acetic acid, boric acid, metaboric acid, succinic acid, citric acid, formic acid, and/or polyacrylic acid may be added to the size composition to assist in the hydrolysis of the silane coupling agent. The sizing composition maintains bundle integrity during the formation and subsequent processing of glass fiber bundles in a wet-laid process to form a chopped strand mat.
Although sizing compositions that do not contain polyvinyl alcohol for use with fibers used in wet-laid processes are known in the art, there remains a need in the art for a sizing composition for wet chopped fibers used in a wet-laid process that reduces or eliminates the formation of precipitates in the white water and maintains or exceeds the dry tensile and tear strengths of wet-laid mats formed with the sized fibers.